Small blood clots during your period are normal and happen when your flow is heavy enough that your body’s natural blood-thinning process can’t keep up. But if you’re passing clots larger than a grape, soaking through a pad or tampon every hour, or noticing clots consistently cycle after cycle, something beyond normal menstruation is likely driving it. Several common conditions can explain why this keeps happening, and most are very treatable once identified.
How Menstrual Clots Form
Your uterine lining sheds during each period, and as that tissue and blood leave your body, your uterus releases natural anticoagulants to keep everything flowing smoothly. When bleeding is heavy or fast, those anticoagulants can’t process all the blood in time. The blood pools, coagulates, and forms the jelly-like clots you see on your pad or in the toilet. This is a purely mechanical process: more blood, more clots.
Small clots, especially on your heaviest days, are common and not a red flag. Clots become a concern when they’re larger than a grape, happen frequently throughout your period, or come alongside periods that last longer than seven days.
Hormonal Imbalances That Thicken the Lining
The most common reason for recurring heavy, clot-filled periods is an imbalance between estrogen and progesterone. During the first half of your cycle, estrogen thickens the uterine lining to prepare for a possible pregnancy. After ovulation, progesterone stabilizes that lining and triggers it to shed in an orderly way. If ovulation doesn’t happen (which is more common than many people realize), progesterone never kicks in. The lining keeps growing in response to estrogen, getting thicker and thicker.
When that overgrown lining finally sheds, there’s simply more tissue and blood to pass, which means heavier flow and more clotting. This pattern, called endometrial hyperplasia, is especially common during perimenopause, in teens whose cycles haven’t regulated yet, and in people with polycystic ovary syndrome (PCOS). It’s also one of the more straightforward causes to treat with hormonal options.
Fibroids and Adenomyosis
Uterine fibroids are noncancerous growths in or on the uterine wall. They’re extremely common, affecting up to 80% of women by age 50. Not all fibroids cause symptoms, but those that grow into the uterine cavity can increase the surface area of the lining, distort how the uterus contracts, and interfere with its ability to stop bleeding efficiently. The result is heavier periods with more clots.
Adenomyosis is a related but distinct condition where the tissue that normally lines the uterus grows into the muscular wall itself. That displaced tissue still responds to your hormones each month: it thickens, breaks down, and bleeds, but now it’s doing so inside the muscle. This makes the uterus enlarge and can cause significantly heavier periods with severe cramping. Many people with adenomyosis describe their clots as large and their pain as sharper than typical period cramps.
Thyroid Problems and Bleeding Disorders
Your thyroid gland helps regulate your menstrual cycle, and when it’s underactive, periods often become heavier and more irregular. Hypothyroidism slows down many body processes, including the hormonal signaling that controls how much lining your uterus builds each month. If you’re also experiencing fatigue, weight changes, or feeling cold all the time, a sluggish thyroid could be contributing to your clotting.
Less commonly, a bleeding disorder may be responsible. Von Willebrand disease, the most common inherited bleeding disorder, affects roughly 1% of the population and is significantly underdiagnosed in women. It impairs the blood’s ability to clot properly, which can make periods unusually heavy from the very first one. If you’ve had heavy, clot-filled periods since your teens, bruise easily, or have had prolonged bleeding after dental work or surgery, a bleeding disorder is worth investigating.
Signs Your Clotting Isn’t Normal
It can be hard to judge your own flow since you have no way of comparing it to anyone else’s. These are concrete markers that suggest your bleeding is heavier than it should be:
- Clot size: Passing clots larger than a grape, especially multiple times per period
- Pad or tampon use: Soaking through a pad or tampon every hour for two or more consecutive hours
- Period length: Bleeding that lasts longer than seven days
- Double protection: Needing to wear a pad and tampon at the same time to manage flow
- Night disruption: Waking up to change pads or tampons overnight
If any of these sound familiar, your periods likely qualify as heavy menstrual bleeding, which affects about one in five women.
The Iron Deficiency Connection
Chronic heavy periods with clotting can quietly drain your iron stores over months or years. Iron deficiency anemia is one of the most common consequences of ongoing heavy menstrual bleeding, and its symptoms often overlap with general life fatigue in ways that make it easy to dismiss. You might feel exhausted all the time, dizzy when you stand up, short of breath during exercise, or notice that your skin looks paler than usual. Many people don’t realize their energy levels are abnormally low until their iron is actually tested and treated.
A simple blood test checking your hemoglobin and ferritin (a protein that stores iron) can reveal whether heavy periods have depleted your reserves. Ferritin can drop well before your hemoglobin does, so even if a basic blood count looks normal, low ferritin alone can cause significant fatigue.
How Heavy Menstrual Bleeding Is Diagnosed
If you bring up clotting or heavy periods with your doctor, expect a thorough medical history first. You’ll be asked about how long your periods last, how often you change pads or tampons, whether you’ve noticed clots and how big they are, and what medications or birth control you use. Tracking your cycle with an app before your appointment gives your doctor much more useful information than trying to recall from memory.
From there, testing typically starts simple and gets more targeted based on what your symptoms suggest. A pelvic exam and blood work (checking for anemia, thyroid function, and sometimes clotting disorders) are standard first steps. An ultrasound can reveal fibroids, adenomyosis, or other structural changes. If those results are inconclusive, a hysteroscopy lets your doctor look directly inside the uterus with a thin camera, and an endometrial biopsy takes a small tissue sample to check for hyperplasia or other cellular changes.
Treatment Options That Reduce Clotting
Treatment depends entirely on what’s causing the heavy bleeding, but for most people, medication is the first approach. A hormonal IUD is one of the most effective options. It releases a small amount of progestin directly into the uterus, which thins the lining over time and dramatically reduces flow. Many people see their periods become much lighter or stop altogether within a few months.
Birth control pills, taken either on a standard monthly schedule or continuously, work by regulating the hormonal cycle and preventing the lining from building up excessively. Oral progestins can serve a similar role for people who can’t or prefer not to use estrogen-containing contraceptives.
For people who need relief from heavy flow without hormones, a medication called tranexamic acid helps the body maintain clots where they’re needed (in the uterine blood vessels) rather than letting them break down too quickly. Studies show it reduces menstrual bleeding by 30 to 55%. You take it only during your period, not every day. Anti-inflammatory medications like ibuprofen can also modestly reduce flow while helping with cramps.
When fibroids or adenomyosis are the cause and don’t respond well to medication, procedures ranging from minimally invasive fibroid removal to, in more severe cases, hysterectomy may be discussed. But most people find significant improvement with medical management alone, especially when the underlying cause is identified early.